Re: [FFmpeg-devel] [PATCH v3 0/1] avformat/demux: fix accurate probing of durations in mpegts/ps

[Nicolas Gaullier <nicolas.gaullier@cji.paris>]

>Envoyé : lundi 22 avril 2024 14:32
>À : ffmpeg-devel@ffmpeg.org
>Objet : Re: [FFmpeg-devel] [PATCH v3 0/1] avformat/demux: fix accurate probing of durations in mpegts/ps
>
>>De : Nicolas Gaullier <nicolas.gaullier@cji.paris> Envoyé : mardi 2 
>>avril 2024 23:26 Objet : [PATCH v3 0/1] avformat/demux: fix accurate 
>>probing of durations in mpegts/ps
>>
>>v3: rebased after ed9363052f4b8b8 applied tonight (add 
>>duration_probesize AVOption)
>>
>>Note: I have no other plan for demux/probing; with these two patches, I can cover my use cases, especially mpegts-concats.
>>
>>For remembering, previous cover-letters:
>>
>>v1--------------------
>>ff_read_packet() is more lightweight, but it leads to important issues when looking for accurate durations.
>>As a side effect, the code looks also simpler with regular av_read_frame() calls.
>>1)Updates in the fate tests do exhibit most of the results.
>>
>>2)See also more directly the case of an audio PES containing many frames:
>>>ffprobe tests/data/lavf/lavf.ts -select_streams a -show_entries 
>>>stream=duration -of flat
>>Before patch:
>>  streams.stream.0.duration="0.757556"
>>After patch:
>>  streams.stream.0.duration="1.018778"
>>
>>3)Here is an additional (commonplace) sample to demonstrate the benefit for twofields-encoded video:
>>>https://0x0.st/HFbm.ts (say h264-50i_mp2.ts)
>>
>>>ffprobe h264-50i_mp2.ts -show_entries stream=duration -of flat
>>Before patch:
>>  streams.stream.0.duration="2.060000"
>>  streams.stream.1.duration="1.176000"
>>After patch:
>>  streams.stream.0.duration="2.080000"
>>  streams.stream.1.duration="1.200000"
>>
>>
>>v2--------------------
>>v1: There was an issue with teletext where resolution is set just once at decoder init (teletext resolution is fixed/hard coded), so it is somewhat fragile: when a demuxer context update occurs, it is lost/overriden by >>avcodec_parameters_to_context(sti->avctx, st->codecpar) in read_frame_internal.
>>They could have been other scenario besides teletext, I don't know.
>>v2: So now at estimate_timings_from_pts, with one or more seeking involved (seeking is detected by the mpegts demuxer and set last_vn=-1, so pmt is forced/updated and results in demuxer context update), it is required to >>preserve the info in codecpar at first.
>>Thanks to Michael for reporting the issue.
>>
>>
>>Nicolas Gaullier (1):
>>  avformat/demux: Fix accurate probing of durations in mpegts/ps
>>
>> libavformat/demux.c                           |  36 ++--
>> tests/ref/fate/concat-demuxer-simple2-lavf-ts | 170 +++++++++---------
>> tests/ref/fate/ts-opus-demux                  |   4 +-
>> 3 files changed, 100 insertions(+), 110 deletions(-)
>
>Ping for review ?
>The patch (https://patchwork.ffmpeg.org/project/ffmpeg/list/?series=11386) still applies on current master.
>Thanks.

Ping ?
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